Ceramic Society of Japan Acta Medica Okayama 1348-6535 134 1 2026 Structural and spectroscopic characterization of keatite (SiO2) 1 4 EN Masami Kanzaki Institute for Planetary Materials, Okayama University Xianyu Xue Institute for Planetary Materials, Okayama University Keatite, a polymorph of silica rare in nature, was synthesized by hydrothermal treatment of silicon and water at 100 MPa and 600 °C. The crystal structure of keatite at 24 °C was refined by the Rietveld method using synchrotron X-ray diffraction data. The obtained structure is consistent with the results of previous studies in which some constraints were imposed during refinements. The 29Si MAS NMR spectrum of keatite shows two peaks at −113.9 and −114.3 ppm, which can be assigned to Si at the Si1 and Si2 sites, respectively. The Raman spectrum of keatite shows a prominent peak at 473 cm−1, which is attributable to the Si–O–Si bending mode of the 5-membered ring. These spectra, reported for the first time, are expected to be valuable for the identification of keatite in synthetic and natural samples. No potential conflict of interest relevant to this article was reported.

The Ceramic Society of Japan Acta Medica Okayama 1882-0743 128 10 2020 Crystal structure of Ca(Fe0.4Si0.6)O2.8 oxygen-deficient perovskite 843 846 EN Masami Kanzaki Institute for Planetary Materials, Okayama University The crystal structure of Ca(Fe3+0.4Si0.6)O2.8 oxygen-deficient perovskite phase synthesized at 12 GPa and 1400 °C was studied using synchrotron powder X-ray diffraction. The phase is isostructural to low-pressure phase of Ca(Al0.4Si0.6)O2.8. The structure was refined by the Rietveld method and is consists of a perovskite-like triple-layer of corner-shared (Fe3+,Si)O6 octahedra and a double-layer of SiO4 tetrahedra those are stacked alternatively in the [111] direction of ideal cubic perovskite. Small degree of Fe3+/Si disorder was detected between two octahedral sites. The structure is compared with other oxygen-deficient perovskites. No potential conflict of interest relevant to this article was reported.